Improvised or homemade explosives (HMEs) were once limited to war zones but have recently become a concern for law enforcement and other first responders in the United States and abroad. Such responders may encounter organized groups or curious “citizen scientists” synthesizing HMEs. Fast and accurate identification of the explosive compound used is of the utmost importance. Common constituents of HMEs include organic and inorganic compounds, sugars, and elemental metals. Many different analytical technologies exist for detecting and quantifying explosive materials; however, the different unregulated and easily obtained compounds used in the devices vary greatly in molecular mass, structure, and physicochemical properties, and no single analytical instrument has the capability to identify them all.
A number of different techniques are available for the identification of explosive compounds. Gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), or Fourier transform infrared spectroscopy (FT-IR) may be used for organic and inorganic compounds while ion chromatography (IC) and capillary electrophoresis (CE) may be used for inorganic ions. Metals can be detected by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) or by X-ray diffraction (XRD). Some compounds require electrospray ionization mass spectroscopy (ESI-MS) to be identified in a sample. These detection techniques have similar shortcomings; they require large, expensive pieces of instrumentation that, with the exception of FT-IR, are not portable. Due to vacuum, power, and gas requirements, the instruments required for these techniques are necessarily centrally located. Thus, the sample must be collected and brought to the laboratory, thereby increasing the amount of time before any analytical information on the identity of the explosive can be obtained and, e.g., provided to first responders.
Additionally, samples may need to undergo preparative techniques, such as filtration or extraction before instrumental analysis can be performed, thereby increasing the total analysis time. This also increases the potential for analytes to be lost through such processes by adsorption onto the filtration medium or degradation of the sample by interaction with the extraction solvent. Samples must also be prepared in sufficient volume (generally at least 200 μL per instrument) to be handled by an auto-sampler.